Searching for Indicators of Excavation Damage Using R Statistics Environment

Understanding the formation and physical characteristics of excavation damage of rock mass is critical for the long-term safety evaluation of deep geological disposal of spent nuclear fuel. In order to develop methods for identifying Excavation Damaged Zone (EDZ), physical and mechanical properties of 132 rock specimens were measured. All together 32 physical properties were measured, of which P- and S-wave velocity in three orthogonal directions and under six levels of axial loading. Derived properties were then calculated from the measured ones, leading to a total of 277 different properties, when accounting for measurement direction and level of axial loading. Considering that not all properties were measured from all specimens, this led to approximately 30 000 combinations of physical properties to shift through. Using R as a tool for the statistical analysis allowed the treatment of the entire dataset in reasonable time, thus providing a screening of existing correlations between different properties of the rock specimens. Furthermore, detailed interpretation could then be focused only on associations of statistical significance, whether or not this was apparent from the data. Best indicators for excavation damage based on this study appear to be electrical resistivity, S-wave velocity, shear impedance, shear modulus and Young’s modulus.